<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div id="app" data-msg="hello world" data-testmsg="hello H5"></div>
  <script>
    console.log(document.querySelector('#app').dataset.msg);// hello world
      console.log(document.querySelector('#app').dataset.testmsg);
  </script>

</body>
</html>